Surface-enhanced Raman scattering (SERS)-based cancer diagnostics is an important analytical tool in early detection of cancer. Current work in SERS focuses on plasmonic nanomaterials that suffer from coagulation, selectivity, and adverse biocompatibility when used in vitro, limiting this research to stand-alone biomolecule sensing. Here we introduce a label-free, biocompatible, ZnO-based, 3D semiconductor quantum probe as a pathway for in vitro diagnosis of cancer. By reducing size of the probes to quantum scale, we observed a unique phenomenon of exponential increase in the SERS enhancement up to ~106 at nanomolar concentration. The quantum probes are decorated on a nano-dendrite platform functionalized for cell adhesion, proliferation, and label-free application. The quantum probes demonstrate discrimination of cancerous and non-cancerous cells along with biomolecular sensing of DNA, RNA, proteins and lipids in vitro. The limit of detection is up to a single-cell-level detection.

A laser-induced periodic surface structure (LIPSS) has attracted research interest for its promising potential in micromachining for microelectronics and microelectromechanical systems. A femtosecond laser-induced periodical surface structure was investigated for polished crystalline silicon. The observed structure is similar to the classical ripples that are characterized by long, nearly parallel lines extending over the entire irradiated area on the metal and silicon surface after continuous or pulsed laser irradiation. The spacing of the ripples nearly equals the irradiation wavelength. The depth of these ripples increases nonlinearly with the fluence of irradiation. The orientation of these periodic structures is perpendicular to the vector of the electric field of the laser beam. It seemed that the pattern formed by a femtosecond laser complies well with conventional models. Unlike the patterns formed by a continuous or nanosecond pulsed laser, however, the spacing of the ripple formed by femtosecond pulses is not influenced by the incident angle of the laser beam. The formula used to predict the ripple spacing in the conventional model does not apply to the femtosecond laser induced ripple structure. A plausible explanation to this phenomenon is proposed. The effect of the pulse repetition rate was studied and it was found that a femtosecond laser oscillator generates the same periodic structure as the amplified laser system.

Cancer stem cells (CSC) can be identified by modifications in their genomic DNA. Here, we report a concept of precisely shrinking an organic semiconductor surface-enhanced Raman scattering (SERS) probe to quantum size, for investigating the epigenetic profile of CSC. The probe is used for tag-free genomic DNA detection, an approach towards the advancement of single-molecule DNA detection. The sensor detected structural, molecular and gene expression aberrations of genomic DNA in femtomolar concentration simultaneously in a single test. In addition to pointing out the divergences in genomic DNA of cancerous and noncancerous cells, the quantum scale organic semiconductor was able to trace the expression of two genes which are frequently used as CSC markers. The quantum scale organic semiconductor holds the potential to be a new tool for label-free, ultra-sensitive multiplexed genomic analysis.

In this article we report the synthesis of nanoparticles using femtosecond laser ablation with MHz pulse frequency at room temperature in air. Nanoparticles agglomerate by fusion, and form interweaving fibrous structures that show certain degree of self-assembly. It is found that there is a threshold-like pulse frequency at which fibrous nanoparticle aggregates start to form. The growth mechanism can be explained by existing theories regarding nanoparticle formation through femtosecond laser ablation. The threshold pulse frequency is in good agreement with the time to start nanoparticle formation, which has been derived numerically by previous analyses.

A unique 3-D nanostructure is generated from pure Ti by a pulsed femtosecond laser. The resulting crystalline TiO 2 nanofibers in a 3-D nanonetwork were found to be significant contributors to surface-enhanced Raman spectroscopy (SERS). Overall, the analytical enhancement factor was calculated to be 1.3 × 10 6 based on a crystal violet dye. Based on our best knowledge as well as SEM, TEM, EDX, and AFM studies, high Raman activity may be occurring by multiple mechanisms including nanogap, nanocluster, and plasmonic hybridization. This important result rivals silver (Ag) and gold (Au) as the most popular SERS substrates. The novelty of our presented work implies a potential approach to prepare traditionally inactive substrates for Raman biomolecular sensing and chemical detection studies. ■ INTRODUCTIONRaman vibrational spectroscopy provides insightful characterization of probed substances by unique Stokes-shifted frequencies. 1,2 Surface-enhanced Raman spectroscopy (SERS) greatly improves the sensitivity of traditional Raman spectroscopy while reducing the laser power and collection time. This has allowed for extensive chemical and biosensing applications including rapid sensing of anthrax, 3 RNA structure analysis, 4 cell mapping, 5 and single molecule detection. 6 The most effective method for enhancing the Raman spectra involves increasing surface electromagnetism (EM) activity. The theoretical enhancement factor (EF, typically from 10 4 to 10 12 ) is due to collective vibration of free electrons. In this model, optimized enhancement may be realized by varying nanoparticle (NP) alloys, nanostructure morphology, density, and/or clusters. 7,8 A further in-depth reasoning for EM enhancement concerns confinement of surface plasmons to features that are smaller than the wavelength of incident light. 9,10 Consequently, nanoscale surface features for SERS are paramount. Traditionally, silver (Ag) requires the least modification for SERS. This is due to its low-loss resonance of free electrons and efficient excitation by visible light. Few other coinage metals (group 1B) and alkali metals (group 1A) can provide comparable enhancements. 11 However, transition metals in general have a different electron distribution which becomes difficult to resonate. Consequently, metals like Ti require sophisticated nanofabrication techniques to activate SERS.Well-developed two-dimensional (2-D) nanomanufacturing techniques have shown Raman enhancement but with drawbacks. For example, the signals from SERS active film coatings are attenuated exponentially with increasing film thickness. As well, the film conformity of ideally 3−10 atomic layers over rough surfaces is very difficult to achieve. 11 In addition, recently published chemical methods to control NP aggregation demand precise solution control while commonly requiring additional stabilizers to regulate surface features. 12,13 On the other hand, three-dimensional (3-D) nanomanufacturing methods have a great potential for high Raman enhancement while maintaining synthesis simpli...

No abstract

Schematic illustration shows remarkable SERS activities of self-doped Q-structured TiOx with oxygen vacancies compared to the Q-structured TiO2.

No abstract